Support substrate for thin-sheet work

ABSTRACT

A magnetic tape or magnetized tape is affixed to one side of a sheet-like workpiece, for example, the front surface of a semiconductor wafer. A substrate has a support area, which is at least partially formed of a porous material and is at least partially magnetized or magnetic.

TECHNICAL FIELD

[0001] The present invention relates to a substrate for supporting asheet-like workpiece such as a semiconductor wafer.

BACKGROUND ART

[0002] As is known to people of ordinary skill in the art, in theproduction of semiconductor chips, a large number of rectangular areasare defined by streets arranged in a lattice form in the front surfaceof a semiconductor wafer, and semiconductor circuits are formed in eachof the rectangular areas. In general, the back surface of thesemiconductor wafer is ground to reduce its thickness and then, thesemiconductor wafer is cut along the streets to separate the rectangularareas from one another, thereby forming semiconductor chips. In recentyears, prior to the grinding of the back surface of the semiconductorwafer, grooves having a required depth have been formed along thestreets from the front surface of the semiconductor wafer and then, theback surface of the semiconductor wafer is ground to reduce thethickness of the semiconductor wafer to a value smaller than the depthof the groove, thus separating the rectangular areas from one another toform semiconductor chips. In either cases, to grind the back surface ofthe semiconductor wafer, a tape is affixed onto the front surface of thesemiconductor wafer to protect the semiconductor circuits, thesemiconductor wafer is held on a chuck means in a state of the frontsurface having the tape affixed thereon facing down, that is, in a stateof the front surface and the back being reversed, and a grinding meansis caused to act on the back surface of the semiconductor wafer. Thesemiconductor wafer is held on the chuck means by sucking thesemiconductor wafer through the holding area that is formed of a porousmaterial, of the chuck means.

[0003] In recent years, in order to form very small-sized andlightweight semiconductor chips, it has often been desired that thethickness of the semiconductor wafer be made very small, for example,100 μm or less, particularly 50 μm or less. When the thickness of thesemiconductor wafer is very small, however, rigidity of thesemiconductor wafer greatly lowers, thereby making it extremelydifficult to carry the semiconductor wafer, for example, from the chuckmeans into a cassette container. When a tape having relatively highrigidity, such as a polyethylene terephthalate film or sheet is used asthe tape to be affixed onto the front surface of the semiconductor waferthrough a suitable adhesive or pressure-sensitive adhesive, thesemiconductor wafer can be carried. However, when a tape havingrelatively high rigidity is affixed onto the front surface of thesemiconductor wafer, it is considerably difficult to remove thesemiconductor chips that have been separated from one another from thetape, without damaging them.

DISCLOSURE OF THE INVENTION

[0004] It is therefore the principal object of the present invention toprovide a substrate for supporting a sheet-like workpiece such as asemiconductor wafer, which makes it possible to carry a semiconductorwafer very easily even when the thickness of the sheet-like workpiece isgreatly reduced by grinding without exerting a bad influence upon thegrinding of the sheet-like workpiece and without the need of affixing atape having relatively high rigidity onto the front surface of thesheet-like workpiece.

[0005] The inventor of the present invention has found that the aboveprincipal object can be attained by using a magnetic tape or magnetizedtape as the tape to be affixed to one surface side of the sheet-likeworkpiece, for example, the front surface of a semiconductor wafer andby using a substrate having a support area that is at least partiallyformed of a porous material and at least partially magnetized ormagnetic.

[0006] That is, according to one aspect of the present invention, thereis provided a substrate for supporting a sheet-like workpiece having amagnetic tape affixed to one surface side thereof, which has a supportarea that is at least partially formed of a porous material and at leastpartially magnetized, as a substrate for attaining the above principalobject.

[0007] Preferably, the support area is formed of a porous materialcontaining a plurality of magnets dispersed therein or is formed of amagnetized porous material. It is advantageous that the substrate shouldhave a frame for surrounding the support area.

[0008] According to another aspect of the present invention, there isprovided a substrate for supporting a sheet-like workpiece having amagnetized tape affixed onto one side thereof, which has a support areathat is at least partially formed of a porous material and at leastpartially magnetic, as a substrate for attaining the above principalobject.

[0009] Preferably, the support area is formed of a porous and magneticmaterial. It is advantageous that the substrate should include a framefor surrounding the support area.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a perspective view of a semiconductor wafer as a typicalexample of a sheet-like workpiece;

[0011]FIG. 2 is a perspective view showing a preferred example of asubstrate constituted according to the present invention;

[0012]FIG. 3 is a perspective view showing a state that thesemiconductor wafer of FIG. 1 is turned upside down and is adsorbed onthe substrate of FIG. 2; and

[0013]FIG. 4 is a sectional view showing a state that the semiconductorwafer adsorbed on the substrate is held on a chuck means of a grindingmachine and the back surface of the semiconductor wafer is ground.

BEST MODE FOR CARRYING OUT THE INVENTION

[0014] Preferred embodiments of a substrate constituted according to thepresent invention will be described in detail with reference to theaccompanying drawings.

[0015]FIG. 1 shows a semiconductor wafer 2 as a typical example of asheet-like workpiece. The illustrated semiconductor wafer 2 is shapedlike a disk having a linear edge 4 called “orientation flat” in partthereof and has a large number of rectangular areas 8 defined by streets6 arranged in a lattice form in its front surface. A semiconductorcircuit is formed in each of the rectangular areas 8. When the thicknessof the semiconductor wafer 2 is to be reduced by grinding the backsurface of the semiconductor wafer 2, a tape 10 is affixed onto thefront surface of the semiconductor wafer 2 to protect the semiconductorcircuits formed in the rectangular areas 8. In the illustratedembodiment, a magnetic tape provided with magnetism by coating the frontsurface and/or the back surface of a synthetic resin film or sheethaving relatively low rigidity, such as a polyolefin film or sheet, withmagnetic powders is used as the tape 10. It is advantageous that thistape 10 be affixed onto the front surface of the semiconductor wafer 2by a known adhesive whose adhesion is lost or reduced by exposure toultraviolet radiation or thermal curing. When the semiconductor chipsare to be removed from the tape 10 after the semiconductor wafer 2 iscut along the streets 6 to separate a plurality of semiconductor chipsfrom one another, the adhesion of the adhesive can be lost or reduced byexposing the tape 10 to ultraviolet radiation or thermally curing it.

[0016]FIG. 2 shows a preferred embodiment of a substrate constitutedaccording to the present invention. The illustrated substrate 12 isshaped like a disk as a whole and comprises a support area 14 at thecenter and a frame 16 surrounding this support area 14. The support area14 has a shape corresponding to the shape of the semiconductor wafer 2and a linear edge 18 corresponding to the linear edge 4 of thesemiconductor wafer 2. It is important that the support area 14 beformed of a porous material. A preferred example of the porous materialforming the support area 14 is porous ceramic. In the illustratedembodiment, a plurality of (6 pieces in the figure) magnets 20 aredispersed and buried in the porous material forming the support area 14.Therefore, the support area 14 is partially magnetized due to theexistence of magnets 20. The frame 16 of the substrate 12 may be formedof a suitable synthetic resin or suitable metal such as stainless steel.The support area 14 and the frame 16 surrounding the support area 14 arefirmly bonded to each other. It is advantageous that the top surface ofthe support area 14 and the top surface of the frame 16 be flush witheach other and that the back surface of the support area 14 and the backsurface of the frame 16 be also flush with each other.

[0017] To grind the back surface of the semiconductor wafer 2, as shownin FIG. 3, the semiconductor wafer 2 having the tape 10 affixed onto thefront surface thereof is placed on the support area 14 of the substrate12 in such a state that the front surface faces down, that is, that thefront surface and the back surface are reversed. Thereby, as the supportarea 14 is partially magnetized by the magnets 20 buried therein, thetape 10 having magnetism and affixed onto the front surface of thesemiconductor wafer 2, the semiconductor wafer 2 is magneticallyadsorbed on the support area 14 of the substrate 12.

[0018] Continuing a description with reference to FIG. 4 together withFIGS. 1 to 3, a grinding machine used for grinding the back surface ofthe semiconductor wafer 2, for example, a grinding machine marketedunder the trade name of DFG841 from DISCO CORPORATION has a chuck means22. The chuck means 22 has a disk-like porous central member 24 and anannular casing 26 surrounding the central member 24. The outer diameterof the central member 24 fixed in the annular casing 26 corresponds tothe outer diameter of the support area 14, that is, to the outerdiameter of the semiconductor wafer 2, and the outer diameter of theannular casing 26 is made to correspond to the outer diameter of theframe 16 of the substrate 12. The top surface of the central member 24and the top surface of the annular casing 26 are flush with each other.As clearly shown in FIG. 4, the substrate 12 which magnetically adsorbsthe semiconductor wafer 2 on the support area 14 is placed on the chuckmeans 22 by aligning the support area 14 with the central member 24. Thecentral member 24 of the chuck means 22 is communicated with a vacuumsource (not shown) through a suitable suction path so that when thevacuum source is activated, air is sucked in through the central member24 of the chuck means 22 and the support area 14 of the substrate 12 toadsorb the semiconductor wafer 2 on the central member 24 of the chuckmeans 22 fully firmly. The exposed back surface of the semiconductorwafer 2 is ground by the function of a grinding means 28. The grindingmeans 28 is constituted by an annular grinding tool having an abrasivemeans containing diamond abrasive grains in the under surface. To grindthe back surface of the semiconductor wafer 2, the chuck means 22holding the semiconductor wafer 2 is turned on its center axis, and thegrinding means 28 is turned on its center axis and pressed against theback surface of the semiconductor wafer 2.

[0019] After the back surface of the semiconductor wafer 2 is ground asrequired, the operation of the vacuum source is stopped to release thesuction operation of the chuck means 22, the substrate 12 and thesemiconductor wafer 2 magnetically adsorbed on the substrate 12 aredisengaged from the chuck means 22, and the semiconductor wafer 2 iscarried to a required position, for example, in a cassette container.When the semiconductor 2 is adsorbed on the substrate 12, the substrate12 and the semiconductor wafer 2 adsorbed on the substrate 12 can becarried by holding a suitable portion, for example, the frame 16 of thesubstrate 12. Therefore, even when the thickness of the semiconductorwafer is greatly reduced and the rigidity of the semiconductor wafer 2is thereby greatly reduced, the semiconductor wafer 2 can be carried asrequired without being damaged. Since the semiconductor wafer 2 isadsorbed on the substrate 14 by the magnetic adsorption of the tape 10affixed onto the front surface of the semiconductor wafer 2, when thesemiconductor wafer 2 is to be removed from the substrate 12, it can beeasily removed from the substrate 12 with relatively small force.

[0020] In the illustrated embodiment, the support area 14 is partiallymagnetized by dispersing a plurality of magnets 20 in the porousmaterial forming the support area 14 of the substrate 12. As desired,magnetic powders may be contained in the entire porous material formingthe support area 14 to entirely magnetize the support area 14, or theentire support area 14 may be formed of a magnetized porous material toentirely magnetize the support area 14.

[0021] Further, if desired, as the tape 10 affixed onto the frontsurface of the semiconductor wafer 2 may be used a magnetized tape whichhas been at least partially magnetized. A typical example of themagnetized tape is a tape prepared by coating the front surface and/orthe back surface of a synthetic resin film or sheet having relativelylow rigidity, such as a polyolefin film or sheet, with magnetic powders.When the tape 10 affixed onto the front surface of the semiconductorwafer 2 is a magnetized tape, the support area 14 of the substrate 12does not need to be magnetized. When the support area 14 is at leastpartially formed of a magnetic material, the magnetized tape 10, thatis, the semiconductor wafer 2 having the magnetized tape on the frontsurface can be magnetically adsorbed on the support area 14 of thesubstrate 12.

1. A substrate for supporting a sheet-like workpiece having a magnetictape affixed onto one side thereof, which has a support area that is atleast partially formed of a porous material and at least partiallymagnetized.
 2. The substrate of claim 1, wherein the support area isformed of a porous material containing a plurality of magnets dispersedtherein.
 3. The substrate of claim 1., wherein the support area isformed of a magnetized porous material.
 4. The substrate of claim 1which has a frame surrounding the support area.
 5. A substrate forsupporting a sheet-like workpiece having a magnetized tape affixed toone side thereof, which has a support area that is at least partiallyformed of a porous material and at least partially magnetic.
 6. Thesubstrate of claim 5, wherein the support area is formed of a porous andmagnetic material.
 7. The substrate of claim 5 which has a framesurrounding the support area.